Device for compensating the head weight on portal or cantilever type machine tools

ABSTRACT

A device for counterbalancing a head slidably mounted on a crossrail in which a cable is secured at one end to the head and the other end of which cable is secured to a cable winch exerting a constant pull on the cable and the head, the winch is resiliently, slidably mounted in the direction of cable pull on a carriage which carriage travels parallel to the direction of travel of the head on the cross rail, means including a feeler sensing the sliding movement of the winch in the cable pull direction is provided for controlling the direction of rotation of the cable winch so as to maintain the winch in a predetermined position of rest, means is also provided for maintaining the carriage travel in alinement with the head travel.

United States Patent Briesofsky [54] DEVICE FOR COMPENSATING TI-IE HEADWEIGHT ON PORTAL OR CANTILEVER TYPE MACHINE TOOLS [72] Inventor: GiinterBriesofsky, Coburg/Bavaria,

Germany [73] Assignee: Werkzeugmaschinenfabrik Adolf Waldrich Coburg,Coburg/Bavaria, Germany [22] Filed: Jan. 27, 1971 [21] Appl. No.:110,040

[30] Foreign Application Priority Data 1 1 Aug. 15, 1972 FOREIGN PATENTSOR APPLICATIONS 507,872 12/1951 Belgium ..90/ll F PrimaryExaminer-Francis S. I-Iusar Attorney-Woodhams, Blanchard and Flynn [57]ABSTRACT A device for counterbalancing a head slidably mounted on acrossrail in which a cable is secured at one end to the head and theother end of which cable is secured to a cable winch exerting a constantpull on the cable and the head, the winch is resiliently, slidablymounted in the direction of cable pull on a carriage which carriagetravels parallel to the direction of travel of the head on the crossrail, means including a feeler sensing the sliding movement of the winchin the cable pull direction is provided for controlling the direction ofrotation of the cable winch so as to maintain the winch in apredetermined position of rest, means is also provided for maintainingthe carriage travel in alinement with the head travel.

8 Claims, 3 Drawing Figures DEVICE FOR COMPENSATING THE HEAD WEIGHT ONPORTAL OR CANTILEVER TYPE MACHINE TOOLS 1 The invention relates to adevice for compensating the head weight on portal or cantilever typemachine to its position of rest in which the motor exerts a contools, inwhich the head is suspended on a cable leading to a carriage slidableabove the cross rail on a stationary cross beam, for example the crosshead, parallel with the cross rail, which carriage is driven insynchronism with the head, the cable being under constant pull.

Owing to the weight of the head or heads, the cross rail of a machinetool is deflected by different amounts depending on the position of thehead. It is therefore necessary to compensate the weight of the heads byvertically upward pull.

In order to achievethis, in a device of the type mentioned above, thecable is passed over stationary rollers and over movable rollerssituated on the carriage, and counterweights are provided on the end ofthe cable. For constructional reasons, however, the cable cannot run inone plane, so that many guide rollers are necessary. If there are two ormore heads, this results in considerable accommodation difficulties,particularly if it is considered that in the case of heads ofconsiderable weight, the counterweights must be of large and heavyconstruction.

Another device is therefore also known, in which the carriage is carriedon an auxiliary girder supported by both ends in the vicinity of theends of the cross rail. Tension springs are provided between thecarriage and the head. This solution also has various disadvantages. Ifthe cross rail is adjusted vertically by means of elevating screws,there are different loads on the screws, depending on the position ofthe head. Elongation of the screws is not compensated. The elevatingscrews have also to be of particularly robust construction and aresubjected to heavy wear because in addition to the weight of the crossrail and heads, they have also to carry the weight of the auxiliarygirder which must also be of particularly robust and therefore heavyconstruction for preventing deflections.

The invention is based on the problem of providing a device of the typementioned in the foregoing which permits the most accurate compensationpossible of the head weight and at the same time is of the mostspacesaving construction possible.

This is achieved according to the invention in that a cable winch,resiliently supported in the pulling direction of the cable, is providedon the carriage, which winch is driven by a motor continuously exertinga constant torque on the winch drum, a feeler, movable in the directionof pull of the cable and connected to a regulator controlling the powersupply to the motor, being provided between the cable winch and carriagefor controlling the motor, such that on a change in position of thecable winch owing to variation in the cable load, the power supply tothe motor is released in one or the other direction of rotation untilthe cable winch has returned to its position of rest. This arrangementeliminates any counterweights. The entire device can be accommodated ona comparatively small carriage so that also the compensation of a numberof heads does not give rise to any difficulties, since a number ofcarriages may be arranged side by side. The feeler with the regulatorand motor together form a regulating circuit which ensures that thecable winch is alwaysretumed stant torque on the cable winch and hence aconstant pull on the cable.

A particularly advantageous embodiment of the subject of the inventionis that an auxiliary girder mounted freely at both ends on the uprightsand independent of the cross-head is provided as cross-girder for thecarriage, only the front carriage guide rail situated nearer to the headbeing preferably mounted on the auxiliary girder, while the moreremotely situated guide rail is fixed to the cross head. The auxiliarygirder then receives the principal supporting load. This obviates thetransmission of bending forces to the uprights, which could affect theaccuracy of the machine tool. Any deflections of the auxiliary girder inthe device according to the invention are without effect on thecompensation of the weight of the head. Independently of the length ofthe pull cable at the time, the device according to the inventionensuresthat the same pull is always exerted on the cable.

Further advantages and details of the invention are explained moreparticularly in the following with reference to an embodiment exampleillustrated in the drawings, in which:

FIG. 1 shows a diagrammatic perspective view of the subject of theinvention,

FIG. 2 shows a side view in the direction II of FIG. 1,

FIG. 3 shows apart plan in the direction III of FIG. 2.

In the drawings, 1 denotes a head slidable on the cross rail 2. Forrelieving the weight load, a cable 3 is fixed to the head 1 in the axisof its center of gravity. The cable is passed over a guide roller 4 tothe cable drum 6 of a cable winch 5, which advantageously is driven by ahydraulic motor 7, possibly with the interposition of a suitablereduction gear 7a. The cable winch 5 is mounted on a slide 12 slidablehorizontally on the carriage 8 in the direction of the cable pull. Theslide is supported on the carriage 8 by compression springs 9. Thecarriage itself is slidably guided, parallel to the cross rail by meansof the rail 11, mounted on the auxiliary girder 13, and the rail 14secured to the cross head 22. The carriage is driven by a hydraulicmotor 17 which engages the rack 15 by means of the pinion 16.Advantageously, the power supply to this hydraulic motor is controlledby means of a regulator 18 which co-operates with a feeler 20 exploringthe deflection of the cable 3, as is described more particularly below.

To bring about compensation of the head weight, it is necessary for thecable 3 to be under a constant pull. For this purpose, the hydraulicmotor 7 is under constant pressure and exerts a constant torque on thecable drum 6. By the pull of the cable winch on the one hand and theforce of the springs 9, a certain position of rest of the slide 12occurs. This position of rest is monitored by a regulator 10 whichcontrols the power supply to the motor 7 and is connected to a feeler10a. The feeler 10a is movable in the direction of pull of the cable andexplores a part of the carriage 8.

If the cross rail is moved downward, the cable winch 5 is at first movedto the left in the direction A, the springs 9 being compressed. Thismovement is detected by the feeler 10a and hydraulic fluid is suppliedto the hydraulic motor 7 by the regulator 10, whereby the cable winch 6is rotated in the direction B. The pull cable 3 is thereby lengtheneduntil the pull on the cable has reached its original value again, andthe springs 9 force the cable winch 5 to the right into its position ofrest. If, on the contrary, the cross rail 2 moves upward, the springs 9force the cable winch 5 to the right. The feeler 10a then adjusts theregulator 10 such that the motor 7 is actuated in the reverse directionof rotation and thus the cable drum is driven opposite to the directionof the arrow B. Here again, supply to the motor 7 continues until theslide 12 has returned to its position of rest again. In the position ofrest, the regula tor 10 still allows so much pressure to occur in thehydraulic motor 7 that the equilibrium of forces between cable force andspring force is re-established, i.e., the hydraulic motor then exerts acorresponding torque. This condition of the hydraulic motor of theregulator will be referred to in what follows as the position orsituation of rest.

A hydraulic motor is advantageously used for driving the cable drum 6since it can be regulated particularly simply and in its position ofrest develops the torque necessary for weight compensation. Instead of ahydraulic motor a suitable electric motor, which develops a holdingtorque when stationary, could possibly also be provided.

The regulating circuit of the motor is advantageously adjusted such thatthe constant pull exerted by the cable winch is greater than the weightof the head. The head is thereby pressed from below in the cutting forcedirection against the guides of the cross rail, thereby ensuring thatthe head always bears against the same guideway, independently of whichcutting force occurs.

The considerable weight of the head, to which there is also added theweight of the carriage and cable winch, results in considerable loadingof the girder on which the carriage is carried. lf the carriage wascarried on the cross head of the machine tool as would be quiteappropriate in the case of smaller weights, greater weights result indeformation of the uprights, thus impairing the working accuracy. Toeliminate this disadvantage also it is expedient if an auxiliary girdermounted freely at both ends on the uprights 21 and independent of thecross-head 22 is provided as crossgirder for the carriage. Thisauxiliary girder may either carry the entire carriage or preferably maybe constructed such that only the front guide rail 11 of the carriage 8,situated closer to the head, is mounted on the said auxiliary girder,while the more remotely situated guide rail 14 is fixed to the crosshead 22. The auxiliary girder 13 then receives the principal supportingload. Owing to this auxiliary girder, bending stresses are then nolonger transmitted to the uprights. The inevitable deflection of theauxiliary girder under the load of the head and carriage has no effecton the magnitude of the pull exerted on the cable, since this pull isalways kept constant by the device described in the foregoing.Deflection of the auxiliary girder would of course be equivalent to anupward movement of the cross rail.

So that the carriage 8 will always be driven in synchronism with thehead a feeler is provided on the carriage or its arm 19, and bearsagainst the cable length extending vertically downward to the head,which feeler is movable in the direction of movement of the carriage andis connected to the regulator 18. Vertical position of the cableexplored by the feeler 20 corresponds to zero position of the regulator18, in which the supply to the hydraulic motor 17 is blocked. If thehead 1 moves, a deflection of the feeler 20 occurs through theself-adjusted inclination of the cable, and the regulator releases powerto the hydraulic motor 17 in the necessary direction until the verticalposition of the cable has again been reached.

The present invention is not restricted to the embodiment example shown.For example, in a head having a slide vertically slidable in theelevating screw direction, known as a slide milling head, it would beadvantageous to fix the cable to the slide.

The result is a permanent weight compensation of the slide carrying thescrew regardless of whether the cross rail or only the slide is moved upor down.

I claim:

1. Device for compensating the head weight on portal or cantilever typemachine tools, in which the head is suspended by a cable which iscarried to a carriage driven synchronously with the head and slidableparallel to and above the cross rail, on a stationarily arrangedcross-girder, for example on the cross head, the

.cable being under constant pull, characterized in that a cable winch(5), resiliently supported in the pulling direction of the cable (3), isprovided on the carriage (8), and is driven by a motor (7) continuouslyexerting a constant torque on the cable drum (6), a feeler (10a) movablein the cable pull direction and connected to a regulator (10)controlling the power supply to the motor (7) being provided between thecable winch (5) and carriage (8) for controlling the motor (7), suchthat on a change in position of the cable winch (5) owing to a change inthe cable load, the power supply to the motor (7 is released in the oneor other direction of rotation until the cable winch (5) has returned toits position of rest.

2. Device according to claim 1, characterized in that the cable winch(5) is mounted on a slide (12) slidable horizontally on the carriage (8)in the cable pull direction.

3. Device according to claim 1, characterized in that a hydraulic motoris provided as cable winch motor 7 4. Device according to claim 1,characterized in that the constant pull exerted by the cable winch (5)is greater than the weight of the head (1 5. Device according to claim1, characterized in that in the case of a head having a slide verticallyslidable in the elevating screw direction, the cable is fixed to theslide.

6. Device according to claim 1, characterized in that an auxiliarygirder (13) mounted freely at both ends of the uprights (21) andindependent of the cross head (22) is provided as cross-girder for thecarriage (8).

7. Device according to claim 1, characterized in that a feeler (20),bearing against the cable length (3) extending vertically on thecarriage (8), is movable in the direction of movement of the carriage(8) and is connected to a regulator (18) controlling the power supply tothe driving motor (17) of the carriage (8) such that on lateraldeflection of the cable (3) due to sliding of the head (1), power supplyis released to the driving motor (17) until the deflection is removed.

8. Device according to claim 6, characterized in that only the frontguide rail (11) of the carriage (8) lying nearer to the head is mountedon the auxiliary girder, I while the more remotely situated guide railis fixed to the cross head (22).

1. Device for compensating the head weight on portal or cantilever typemachine tools, in which the head is suspended by a cable which iscarried to a carriage driven synchronously with the head and slidableparallel to and above the cross rail, on a stationarily arrangedcross-girder, for example on the cross head, the cable being underconstant pull, characterized in that a cable winch (5), resilientlysupported in the pulling direction of the cable (3), is provided on thecarriage (8), and is driven by a motor (7) continuously exerting aconstant torque on the cable drum (6), a feeler (10a) movable in thecable pull direction and connected to a regulator (10) controlling thepower supply to the motor (7) being provided between the cable winch (5)and carriage (8) for controlling the motor (7), such that on a change inposition of the cable winch (5) owing to a change in the cable load, thepower supply to the motor (7) is released in the one or other directionof rotation until the cable winch (5) has returned to its position ofrest.
 2. Device according to claim 1, characterized in that the cablewinch (5) is mounted on a slide (12) slidable horizontally on thecarriage (8) in the cable pull direction.
 3. Device according to claim1, characterized in that a hydraulic motor is provided as cable winchmotor (7).
 4. Device according to claim 1, characterized in that theconstant pull exerted by the cable winch (5) is greater than the weightof the head (1).
 5. Device according to claim 1, characterized in thatin the case of a head having a slide vertically slidable in theelevating screw direction, the cable is fixed to the slide.
 6. Deviceaccording to claim 1, characterized in that an auxiliary girder (13)mounted freely at both ends of the uprights (21) and independent of thecross head (22) is provided as cross-girder for the carriage (8). 7.Device according to claim 1, characterized in that a feeler (20),bearing against the cable length (3) extending vertically on thecarriage (8), is movable in the direction of movement of the carriage(8) and is connected to a regulator (18) controlling the power supply tothe driving motor (17) of the carriage (8) such that on lateraldeflection of the cable (3) due to sliding of the head (1), power supplyis released to the driving motor (17) until the deflection is removed.8. Device according to claim 6, characterized in that only the frontguide rail (11) of the carriage (8) lying nearer to the head is mountedon the auxiliary girder, while the more remotely situated guide rail isfixed to the cross head (22).